Function getKroneckerProduct

tests/utils/linalg.cpp:523–544

qmatrix getKroneckerProduct(qmatrix a, qmatrix b) {

    // we permit the matrices to be non-square which is
    // pretty cheeky (since qmatrix is assumed square with
    // a 2^N dimension by most other functions), but is
    // necessary for us to compute partial traces

    size_t aRows = a.size();
    size_t bRows = b.size();
    size_t aCols = a[0].size();
    size_t bCols = b[0].size();

    qmatrix out(aRows * bRows, qvector(aCols * bCols));
    
    for (size_t r=0; r<bRows; r++)
        for (size_t c=0; c<bCols; c++)
            for (size_t i=0; i<aRows; i++)
                for (size_t j=0; j<aCols; j++)
                    out[r+bRows*i][c+bCols*j] = a[i][j] * b[r][c];

    return out;
}


qmatrix getKroneckerProduct(vector<qmatrix> matrices) {